Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Immunization with a particulate fraction of blood-stage antigens was shown previously to protect mice against Plasmodium yoelii malaria. To identify antigens inducing the protective response, sera from immunized mice were used to screen a P. yoelii cDNA expression library. Sequence analysis of one 2.6-kb cDNA clone indicated that the identified gene, pypag-1, encoded a novel plasmodial antigen. Two nonoverlapping regions of pypag-1 were expressed in Escherichia coli. The first recombinant antigen, pAg-1N, contained the N-terminal 337 residues, which included a putative transmembrane domain and a region relatively rich in tryptophan residues. The second recombinant antigen, pAg-1C, contained the remaining C-terminal 211 residues, which included 31 copies of a 5-amino-acid degenerative repeat. Immunoblot studies using rabbit antiserum raised against recombinant pAg-1N showed that the native pypAg-1 protein migrated at approximately 98 kDa, considerably slower than its predicted molecular mass of 66 kDa. Immunofluorescence studies localized the expression of the native pypAg-1 protein both to the cytoplasm and at the surface of P. yoelii-infected erythrocytes. Immunization with either pAg-1N or pAg-1C induced a four- to sevenfold reduction in P. yoelii blood-stage parasitemia. As such, pypAg-1 appears to contain at least two distinct protective epitopes. To our knowledge, this is the first characterization of a protective antigen of P. yoelii that is associated with the erythrocyte membrane.
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PMID:Protective immunization with a novel membrane protein of Plasmodium yoelii-infected erythrocytes. 991 76

A new general strategy for the production of recombinant protein immunogens has been investigated. The rationale involves the production of a recombinant immunogen as fused to a composite tag comprising one domain suitable for affinity purification and a hydrophobic tag designed for direct incorporation through hydrophobic interaction of the affinity-purified immunogen into an adjuvant system, in this case immunostimulating complexes (iscoms). Three different hydrophobic tags were evaluated: (i) a tag denoted IW containing stretches of hydrophobic isoleucine (I) and tryptophan (W) residues; (ii) a tag denoted MI consisting of the transmembrane region of hemagglutinin from influenza A virus; and (iii) a tag denoted PD designed to be pH-dependent in such a way that an amphiphatic alpha-helix would be formed at low pH. As an affinity tag, an IgG-binding domain Z derived from Staphylococcus aureus protein A (SpA) was used, and a malaria peptide M5, derived from the central repeat region of the Plasmodium falciparum blood-stage antigen Pf155/RESA, served as a model immunogen in this study. Three different fusion proteins, IW-Z-M5, MI-Z-M5 and PD-Z-M5, were produced in Escherichia coli, and after affinity purification these were evaluated in iscom-incorporation experiments. Two of the fusion proteins, IW-Z-M5 and MI-Z-M5 were found in the iscom fraction following preparative ultracentrifugation, indicating iscom incorporation. This was further supported by electron microscopy analysis showing that iscoms were formed. Furthermore, these iscom preparations were demonstrated to induce efficient M5-specific antibody responses upon immunization of mice, confirming successful incorporation into iscoms. The implications of these results for the design and production of subunit vaccines are discussed.
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PMID:General expression vectors for production of hydrophobically tagged immunogens for direct iscom incorporation. 1002 83

The pathogenesis of cerebral malaria is poorly understood. One hypothesis is that activation of microglia and astrocytes in the brain might cause the cerebral symptoms by excitotoxic mechanisms. Cerebrospinal fluid was sampled in 97 Kenyan children with cerebral malaria, 85% within 48 hr of admission. When compared with an age-matched reference range, there were large increases in concentrations of the excitotoxin quinolinic acid (geometric mean ratio cerebral malaria/reference population [95% confidence limits] = 14.1 [9.8-20.4], P < 0.001) and total neopterin (10.9 [9.1-13.0], P < 0.001) and lesser increases in tetra-hydrobiopterin, di-hydrobiopterin, and 5-hydroxyindoleacetic acid. There was no change in tryptophan concentration. In contrast, nitrate plus nitrite concentrations were decreased (geometric mean ratio = 0.45 [0.35-0.59], P < 0.001). There was a graded increment in quinolinic acid concentration across outcome groups of increasing severity. The increased concentration of quinolinic acid suggests that excitotoxic mechanisms may contribute to the pathogenesis of cerebral malaria.
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PMID:Cerebrospinal fluid studies in children with cerebral malaria: an excitotoxic mechanism? 1081 86

Sex is an obligate step in the life cycle of the malaria parasite and occurs in the midgut of the mosquito vector. With both Plasmodium falciparum and Plasmodium berghei, the tryptophan metabolite xanthurenic acid induces the release of motile male gametes from red blood cells (exflagellation), a prerequisite for fertilization. The addition of cGMP or phosphodiesterase inhibitors to cultures of mature gametocytes has also been shown to stimulate exflagellation. Here, we demonstrate that there is a guanylyl cyclase activity associated with mature P. falciparum gametocyte membrane preparations, which is dependent on the presence of Mg(2+)/Mn(2+) but is inhibited by Ca(2+). Significantly, this activity is increased on addition of xanthurenic acid. In contrast, a xanthurenic acid precursor (3-hydroxykynurenine), which is not an inducer of exflagellation, does not induce this guanylyl cyclase activity. These results therefore suggest that xanthurenic acid-induced exflagellation may be mediated by activation of the parasite cGMP signalling pathway.
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PMID:The gametocyte-activating factor xanthurenic acid stimulates an increase in membrane-associated guanylyl cyclase activity in the human malaria parasite Plasmodium falciparum. 1170 75

Kynurenine 3-hydroxylase (K3H) is a NADPH-dependent flavin monooxygenase involved in the tryptophan pathway. Xanthurenic acid (XA) is a metabolite of this pathway and has recently been identified as a gamete activating factor (GAF) of the malarial parasite. We cloned K3H cDNA from Anopheles stephensi (AsK3H), because anopheline mosquitoes are a vector of the human malaria parasite, Plasmodium falciparum and the catalytic function of AsK3H in XA production. Recombinant AsK3H protein was expressed in Sf-9 cells using the baculovirus system and its enzymatic properties were characterized. The specific activities of crude cell lysate and affinity purified protein were 94.9 +/- 6.2 and 865.6 +/- 10.5 nmol/min/mg protein, respectively. The optimum pH of AsK3H was 7.0. Analysis of AsK3H gene expression using RT-PCR revealed that AsK3H was constitutively expressed in egg, larva, pupa and adult.
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PMID:cDNA cloning, functional expression and characterization of kynurenine 3-hydroxylase of Anopheles stephensi (Diptera: Culicidae). 1223 May 48

The protozoan parasite Plasmodium causes malaria, with hundreds of millions of cases recorded annually. Protection against malaria infection can be conferred by antibodies against merozoite surface protein (MSP)-1, making it an attractive vaccine candidate. Here we present the structure of the C-terminal domains of MSP-1 (known as MSP-1(19)) from Plasmodium knowlesi. The structure reveals two tightly packed epidermal growth factor-like domains oriented head to tail. In domain 1, the molecule displays a histidine binding site formed primarily by a highly conserved tryptophan. The protein carries a pronounced overall negative charge primarily due to the large number of acidic groups in domain 2. To map protein binding surfaces on MSP-1(19), we have analyzed the crystal contacts in five different crystal environments, revealing that domain 1 is highly preferred in protein-protein interactions. A comparison of MSP-1(19) structures from P. knowlesi, P. cynomolgi, and P. falciparum shows that, although the overall protein folds are similar, the molecules show significant differences in charge distribution. We propose the histidine binding site in domain 1 as a target for inhibitors of protein binding to MSP-1, which might prevent invasion of the merozoite into red blood cells.
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PMID:Structure of the C-terminal domains of merozoite surface protein-1 from Plasmodium knowlesi reveals a novel histidine binding site. 1249 33

A neural network approach for the prediction of mitochondrial transit peptides (mTPs) from the malaria-causing parasite Plasmodium falciparum is presented. Nuclear-encoded mitochondrial protein precursors of P. falciparum were analyzed by statistical methods, principal component analysis and supervised neural networks, and were compared to those of other eukaryotes. A distinct amino acid usage pattern has been found in protein encoding regions of P. falciparum: glycine, alanine, tryptophan and arginine are under-represented, whereas isoleucine, tyrosine, asparagine and lysine are over-represented compared to the SwissProt average. Similar patterns were observed in mTPs of P. falciparum. Using principal component analysis (PCA), mTPs from P. falciparum were shown to differ considerably from those of other organisms. A neural network system (PlasMit) for prediction of mTPs in P. falciparum sequences was developed, based on the relative amino acid frequency in the first 24 N-terminal amino acids, yielding a Matthews correlation coefficient of 0.74 (90% correct prediction) in a 20-fold cross-validation study. This system predicted 1177 (22%) mitochondrial genes, based on 5334 annotated genes in the P. falciparum genome. A second network with the same topology was trained to give more conservative estimate. This more stringent network yielded a Matthews correlation coefficient of 0.51 (84% correct prediction) in a 10-fold cross-validation study. It predicted 381 (7.1%) mitochondrial genes, based on 5334 annotated genes in the P. falciparum genome.
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PMID:Properties and prediction of mitochondrial transit peptides from Plasmodium falciparum. 1459 65

Products of the kynurenine pathway of tryptophan metabolism have been implicated in the pathogenesis of murine and human cerebral malaria. Indoleamine 2,3-dioxygenase is the first and rate-limiting enzyme in this pathway and we have developed an immunohistochemical method for its detection in tissues from normal and malaria-infected mice. Mice were infected with Plasmodium berghei ANKA, a murine model of cerebral malaria, or P. berghei K173, a non-cerebral malaria model. Vascular endothelial cells were the primary sites of indoleamine 2,3-dioxygenase expression in both types of malaria infection and this response was systemic, with positive staining of vascular endothelium in all tissues examined. No indoleamine 2,3-dioxygenase expression was detected in uninfected or interferon-gamma-/- mice. Corroborative data were obtained using quantitative reverse transcription PCR for indoleamine 2,3-dioxygenase mRNA. These results suggest that interferon-gamma-dependent indoleamine 2,3-dioxygenase expression is part of a normal systemic host response to the parasite, perhaps performing some tissue protective functions that may become deranged under some circumstances and contribute to the pathogenesis of cerebral malaria. On the other hand, constitutive indoleamine 2,3-dioxygenase expression in the epididymis and the placenta was detected in both C57Bl/6 wild-type and interferon-gamma-/- mice, suggesting a distinct regulatory mechanism for its induction in these normal physiological situations. Although increased indoleamine 2,3-dioxygenase production during murine malaria infection may not by itself cause cerebral pathology, metabolites of the kynurenine pathway may combine with other features of cerebral malaria, such as breakdown of the blood-brain barrier, to influence CNS function and contribute to the symptoms and pathology observed.
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PMID:Increased expression of indoleamine 2,3-dioxygenase in murine malaria infection is predominantly localised to the vascular endothelium. 1554 91

Plasmodium vivax is most common but non-cultivable human malaria parasite which is poorly characterized at the molecular level. Here, we describe the identification and characterization of a P. vivax Tryptophan-Rich Antigen (PvTRAg) which contains unusually high (8.28%) tryptophan residues and is expressed by all blood stages of the parasite. The pvtrag gene comprises a 978bp open reading frame interrupted by two introns. The first intron is located in the 5'-untranslated region while the second one is positioned 174bp downstream to the ATG codon. The encoded approximately 40kDa protein contains a transmembrane domain near the N-terminus followed by a tryptophan-rich domain with significantly high surface probability and antigenic index. It is localized in the parasite cytoplasm as well as in the cytoplasm of the parasitized erythrocyte. The purified E. coli expressed recombinant PvTRAg protein showed a very high seropositivity rate for the presence of antibodies amongst the P. vivax patients, indicating that the antigen generates significant humoral immune response during the natural course of P. vivax infection. Analysis of various field isolates revealed that the tryptophan-rich domain is highly conserved except for three-point mutations. The PvTRAg could be a potential vaccine candidate since similar tryptophan-rich antigens of P. yoelii have shown protection against malaria in murine model.
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PMID:Identification, expression, localization and serological characterization of a tryptophan-rich antigen from the human malaria parasite Plasmodium vivax. 1586 15

Intraerythrocytic malaria parasites develop in a highly synchronous manner. We have previously shown that the host hormone melatonin regulates the circadian rhythm of the rodent malaria parasite, Plasmodium chabaudi, through a Ca2+-based mechanism. Here we show that melatonin and other molecules derived from tryptophan, i.e. N-acetylserotonin, serotonin and tryptamine, also modulate the cell cycle of human malaria parasite P. falciparum by inducing an increase in cytosolic free Ca2+. This occurs independently of the extracellular Ca2+ concentration, indicating that these molecules induce Ca2+ mobilization from intracellular stores in the trophozoite. This in turn leads to an increase in the proportion of schizonts. The effects of the indolamines in increasing cytosolic free Ca2+ and modulating the parasite cell cycle are both abrogated by an antagonist of the melatonin receptor, luzindole, and by the phospholipase inhibitor, U73122.
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PMID:Products of tryptophan catabolism induce Ca2+ release and modulate the cell cycle of Plasmodium falciparum malaria parasites. 1615 Jan 1


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